This would be good as block.body().sync_aggregate() so that it works for all post-Altair block types, but I realise that the sync_aggregate method doesn't exist yet in unstable.

When we implement the next fork we should audit all uses of as_altair anyway, so I'm happy to merge without fixing this.

The definition of sync_aggregate is:

impl<'a, T: EthSpec> BeaconBlockBodyRef<'a, T> {
    /// Access the sync aggregate from the block's body, if one exists.
    pub fn sync_aggregate(self) -> Option<&'a SyncAggregate<T>> {
        match self {
            BeaconBlockBodyRef::Base(_) => None,
            BeaconBlockBodyRef::Altair(inner) => Some(&inner.sync_aggregate),
        }
    }
}

in beacon_block_body.rs

Oh, great idea. I hadn't considered this problem before. I've added this function in 0dc02e5. Thanks for laying it all out nicely for me 🙂

Noice 😎